The widespread use of radar and modern navigation aids such as GPS and electronic charts has greatly improved maritime safety. However, even with these tools, the modern navigator is faced with challenges of ever increasing maritime traffic. Not only is traffic increasing, but so to are the size of such vessels.
The presence of nearby moving surface vessels greatly complicates the task of finding a safe and timely path to a destination. In many situations it may not be judicious to simply plot a straight course and handle encounters with other vessels as they occur.
Whereas with passage over streets and highways, the physical structures impose restraints on where vehicles will be and when paths are likely to cross, in the maritime environment there is a great deal more flexibility as well as ambiguity. In addition, the turning radius and minimum distances required to alter heading or significantly change speed are often quite large, especially for large vessels. As such, plotting a straight course with the intention of altering course on a ‘come-as-what-may’ basis may well result in unexpected time delays, increased fuel consumption and wear and tear on physical systems.
Route planning, especially in the maritime environment, typically requires the navigator to plot a course with the anticipation of two, three or even more encounters over relatively short intervals of time. In order to accomplish this task the navigator must visualize dynamic navigation geometry and be able to quickly adapt to changes in information. These changes may include initial detection of nearby vessels, updates in the speed and heading of known nearby vessels, as well as other factors. As this information can and often does change quite rapidly, the navigator will frequently be called upon to make rapid changes and revisions to the planned route of the ship over the entire course of the planned route.
The general approach used in maritime route-planning is to select an ordered set of waypoints, starting at the present position and ending at a destination. These waypoints are selected so that the route that results from the piece-wise linear path obtained by sequentially passing through these waypoints is feasible and efficient. A path is feasible if it observes specified maneuverability constraints and if it avoids obstacles, restricted areas, and applicable navigation rules. A path is efficient if by some measure, there are not other feasible routes that are superior. The measure used may for instance be transit time, route length, number of course changes, the probability of colliding with an obstacle, or some combination. Obstacles may be described as a bounded area such as an ellipse, or they may be described as a two-dimensional probability density.
Although such a problem can be mathematically formulated without much difficulty, there are currently no known general existence and uniqueness theorems or characterizations of optimal solutions that may be applied. Indeed, although an optimal solution may be found through enumeration, the time needed to generate a solution will in most cases render the solution moot in applicability.
This computational difficulty is magnified by the fact that the navigator may not have knowledge of the navigational intentions of nearby vessels. In arriving at a planned route that is both safe and feasible, the navigator is therefore required to predict the future course and speed of these vessels. This forces the navigator to utilize planning intervals that are typically quite small. The result is that the resulting route is usually inefficient.
Planning a route for one short interval after another without attempting to perceive the overall route and how each segment is involved can have drawbacks, as the navigator may not properly perceive or identify trends or issues that are likely to be of significant concern at a future time. In other words the aggregate effect if implemented all at once is likely to be experienced more profoundly then are the small modifications made in each planning interval.
Hence, there is a need for a route-planning navigation system that overcomes one or more of the issues and problems identified above.